The Kunitz-protease inhibitor domain in amyloid precursor protein reduces cellular mitochondrial enzymes expression and function (original) (raw)
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Mitochondrial accumulation of APP and Aβ: significance for Alzheimer disease pathogenesis
Journal of Cellular and Molecular Medicine, 2009
Accumulating evidence suggest that alterations in energy metabolism are among the earliest events that occur in the Alzheimer disease (AD) affected brain. Energy consumption is drastically decreased in the AD-affected regions of cerebral cortex and hippocampus pointing towards compromised mitochondrial function of neurons within specific brain regions. This is accompanied by an elevated production of reactive oxygen species contributing to increased rates of neuronal loss in the AD-affected brain regions. In this review, we will discuss the role of mitochondrial function and dysfunction in AD. We will focus on the consequences of amyloid precursor protein and amyloid- peptide accumulation in mitochondria and their involvement in AD pathogenesis. Fig. 2 A1-40 and A1-42 are taken up by mitochondria through the TOM machinery. After import most of the A will reside in the inner mitochondrial membrane, where it possibly can inhibit the respiration chain (CI-V) resulting in an increased production of ROS. However, a fraction will also reach the matrix where it either can be degraded by proteases like PreP and IDE or interact with proteins such as CypD and ABAD.
Journal of Bioenergetics and Biomembranes, 2009
Several lines of evidence suggest mitochondrial dysfunction as a possible underlying mechanism of Alzheimer's disease (AD). Accumulation of the amyloid-β peptide (Aβ), a neurotoxic peptide implicated in the pathogenesis of AD, has been detected in brain mitochondria of AD patients and AD transgenic mouse models. In vitro evidence suggests that the Aβ causes mitochondrial dysfunction e.g. oxidative stress, mitochondrial fragmentation and decreased activity of cytochrome c oxidase and TCA cycle enzymes. Here we review the link between mitochondrial dysfunctions and AD. In particular we focus on the mechanism for Aβ uptake by mitochondria and on the recently identified Aβ degrading protease in human brain mitochondria.
Acta Neuropathologica
Several lines of recent evidence indicate that the amyloid precursor protein-derived C-terminal fragments (APP-CTFs) could correspond to an etiological trigger of Alzheimer’s disease (AD) pathology. Altered mitochondrial homeostasis is considered an early event in AD development. However, the specific contribution of APP-CTFs to mitochondrial structure, function, and mitophagy defects remains to be established. Here, we demonstrate in neuroblastoma SH-SY5Y cells expressing either APP Swedish mutations, or the β-secretase-derived APP-CTF fragment (C99) combined with β- and γ-secretase inhibition, that APP-CTFs accumulation independently of Aβ triggers excessive mitochondrial morphology alteration (i.e., size alteration and cristae disorganization) associated with enhanced mitochondrial reactive oxygen species production. APP-CTFs accumulation also elicit basal mitophagy failure illustrated by enhanced conversion of LC3, accumulation of LC3-I and/or LC3-II, non-degradation of SQSTM1/p...
Mitochondrial Proteome Changes Correlating with β-Amyloid Accumulation
Molecular Neurobiology, 2016
Alzheimer's disease (AD) is a multifactorial disease of wide clinical heterogenity. Overproduction of amyloid precursor protein (APP) and accumulation of β-amyloid (Aβ) and tau proteins are important hallmarks of AD. The identification of early pathomechanisms of AD is critically important for discovery of early diagnosis markers. Decreased brain metabolism is one of the earliest clinical symptoms of AD that indicate mitochondrial dysfunction in the brain. We performed the first comprehensive study integrating synaptic and non-synaptic mitochondrial proteome analysis (two-dimensional differential gel electrophoresis (2D-DIGE) and mass spectrometry) in correlation with Aβ progression in APP/PS1 mice (3, 6, and 9 months of age). We identified changes of 60 mitochondrial proteins that reflect the progressive effect of APP overproduction and Aβ accumulation on mitochondrial processes. Most of the significantly affected proteins play role in the mitochondrial electron transport chain, citric acid cycle, oxidative stress, or apoptosis. Altered expression levels of Htra2 and Ethe1, which showed parallel changes in different age groups, were confirmed also by Western blot. The common regulator bioinformatical analysis suggests the regulatory role of tumor necrosis factor (TNF) in Aβ-mediated mitochondrial protein changes. Our results are in accordance with the previous postmortem human brain proteomic studies in AD in the case of many proteins. Our results could open a new path of research aiming early mitochondrial molecular mechanisms of Aβ accumulation as a prodromal stage of human AD.
Amyloid-β-Peptide Reduces the Expression Level of Mitochondrial Cytochrome Oxidase Subunits
Neurochemical Research, 2007
Mitochondrial dysfunction is an important cause of neurological disorder including Alzheimer's disease (AD). Mitochondria play a key role in the generation of reactive oxygen species (ROS), resulting in oxidative damage to neuronal cell and cellular compartments in the AD brain. Cytotoxicity induced by amyloid-beta (Ab), a protein fragment of 25-35 amino acids in amyloid plaques has been shown to have neuro-toxic properties. They seem to involve mitochondrial dysfunction, but the underlying mechanisms are not clearly understood. The purpose of this study was to assess whether Ab induced mitochondrial dysfunction involves changes in cytochrome c oxidase (COX) expression. We measured the activities of COX after expose of SK-N-SH cells (a human neuroblastoma cell line) to Ab. We found that levels of mRNAs expressing mitochondrial COX subunits decreased significantly in Ab-treated SK-N-SH cells in a dose-dependent manner. Human mitochondrial transcription factor-1 (TFAM) mRNA level also decreased after Ab-treatment. These results suggest that Ab modulates the mitochondrial gene expression through a decrease in TFAM.
β-Amyloid inhibits integrated mitochondrial respiration and key enzyme activities
Journal of Neurochemistry, 2001
Disrupted energy metabolism, in particular reduced activity of cytochrome oxidase (EC 1.9.3.1), a-ketoglutarate dehydrogenase (EC 1.2.4.2) and pyruvate dehydrogenase (EC 1.2.4.1) have been reported in post-mortem Alzheimer's disease brain. b-Amyloid is strongly implicated in Alzheimer's pathology and can be formed intracellularly in neurones. We have investigated the possibility that b-amyloid itself disrupts mitochondrial function. Isolated rat brain mitochondria have been incubated with the b-amyloid alone or together with nitric oxide, which is known to be elevated in Alzheimer's brain. Mitochondrial respiration, electron transport chain complex activities, a-ketoglutarate dehydrogenase activity and pyru-vate dehydrogenase activity have been measured. b-Amyloid caused a signi®cant reduction in state 3 and state 4 mitochondrial respiration that was further diminished by the addition of nitric oxide. Cytochrome oxidase, a-ketoglutarate dehydrogenase and pyruvate dehydrogenase activities were inhibited by b-amyloid. The K m of cytochrome oxidase for reduced cytochrome c was raised by b-amyloid. We conclude that b-amyloid can directly disrupt mitochondrial function, inhibits key enzymes and may contribute to the de®ciency of energy metabolism seen in Alzheimer's disease.
Degradation of the Amyloid β-Protein by the Novel Mitochondrial Peptidasome, PreP
Journal of Biological Chemistry, 2006
Recently we have identified the novel mitochondrial peptidase responsible for degrading presequences and other short unstructured peptides in mitochondria, the presequence peptidase, which we named PreP peptidasome. In the present study we have identified and characterized the human PreP homologue, hPreP, in brain mitochondria, and we show its capacity to degrade the amyloid -protein (A). PreP belongs to the pitrilysin oligopeptidase family M16C containing an inverted zincbinding motif. We show that hPreP is localized to the mitochondrial matrix. In situ immuno-inactivation studies in human brain mitochondria using anti-hPreP antibodies showed complete inhibition of proteolytic activity against A. We have cloned, overexpressed, and purified recombinant hPreP and its mutant with catalytic base Glu 78 in the inverted zinc-binding motif replaced by Gln. In vitro studies using recombinant hPreP and liquid chromatography nanospray tandem mass spectrometry revealed novel cleavage specificities against A-(1-42), A-(1-40), and A Arctic, a protein that causes increased protofibril formation an early onset familial variant of Alzheimer disease. In contrast to insulin degrading enzyme, which is a functional analogue of hPreP, hPreP does not degrade insulin but does degrade insulin B-chain. Molecular modeling of hPreP based on the crystal structure at 2.1 Å resolution of AtPreP allowed us to identify Cys 90 and Cys 527 that form disulfide bridges under oxidized conditions and might be involved in redox regulation of the enzyme. Degradation of the mitochondrial A by hPreP may potentially be of importance in the pathology of Alzheimer disease.
Degradation of the Amyloid beta-Protein by the Novel Mitochondrial Peptidasome, PreP
Journal of Biological Chemistry, 2006
Recently we have identified the novel mitochondrial peptidase responsible for degrading presequences and other short unstructured peptides in mitochondria, the presequence peptidase, which we named PreP peptidasome. In the present study we have identified and characterized the human PreP homologue, hPreP, in brain mitochondria, and we show its capacity to degrade the amyloid -protein (A). PreP belongs to the pitrilysin oligopeptidase family M16C containing an inverted zincbinding motif. We show that hPreP is localized to the mitochondrial matrix. In situ immuno-inactivation studies in human brain mitochondria using anti-hPreP antibodies showed complete inhibition of proteolytic activity against A. We have cloned, overexpressed, and purified recombinant hPreP and its mutant with catalytic base Glu 78 in the inverted zinc-binding motif replaced by Gln. In vitro studies using recombinant hPreP and liquid chromatography nanospray tandem mass spectrometry revealed novel cleavage specificities against A-(1-42), A-(1-40), and A Arctic, a protein that causes increased protofibril formation an early onset familial variant of Alzheimer disease. In contrast to insulin degrading enzyme, which is a functional analogue of hPreP, hPreP does not degrade insulin but does degrade insulin B-chain. Molecular modeling of hPreP based on the crystal structure at 2.1 Å resolution of AtPreP allowed us to identify Cys 90 and Cys 527 that form disulfide bridges under oxidized conditions and might be involved in redox regulation of the enzyme. Degradation of the mitochondrial A by hPreP may potentially be of importance in the pathology of Alzheimer disease.